1. Field of the Invention
This invention relates to an improved expanded sheet reinforcing material and more particularly to an expanded formable sheet material having a layer of a foamable adhesive adhered to selected surfaces, to methods of manufacturing such expanded sheet material, to methods of reinforcing articles and articles reinforced with such sheet reinforcing material.
2. Description of the Prior Art
Expanded formable sheet material is well-known and widely used for a variety of purposes and apparatus is commercially available for making such expanded sheet material either in a continuous or intermittent operation. In the continuous type of expanding apparatus, an elongated sheet or strip of formable material, for example sheet plastic, steel, aluminum, copper, and other formable material sometimes referred to hereinafter generally as structural sheet material, is fed past a slitting station where a series of parallel, laterally spaced, longitudinally off-set rows of slits are formed through the sheet. The slit sheet is then expanded, or strected in a direction transverse to the direction of movement through the apparatus to separate or open the slits. The expanded sheet material may then be coiled or cut into individual sheets, as desired.
The intermittent process, widely used in the production of expanded sheet metal, involves the use of a die having a plurality of spaced shearing sections or teeth which form the slits by shearing the sheet transverse to its width and simultaneously press the sheared portions of the metal downwardly out of the plane of the unsheared sheet to expand the metal. After each shearing and forming stroke, the die is retracted and either the die or the sheet is moved laterally and the sheet is indexed forward before the next shearing and expanding stroke of the die. This intermittent sheet expanding method, preferred in the practice of the present invention, is generally disclosed in U.S. Pat. Nos. 1,448,109 and 1,561,272.
Various configurations of the die can be used in the intermittent apparatus to provide various shapes of openings as well as different configurations of the strands and joints in the expanded material, though the conventional expanded metal is formed with generally diamond-shaped openings defined by substantially straight-sided strands and joints. In the description of the present invention, the openings will be referred to as generally diamond-shaped, it being understood that the exact configuration is not critical and that such description is intended to include openings of various configurations defined by the interconnected strands and joints.
It is known to employ expanded sheet metal as a stiffener or reinforcing laminate for articles made of sheet metal by attaching the expanded material directly to a surface of the sheet. This concept is shown, for example, in U.S. Pat. No. 2,349,907 wherein flat-rolled expanded sheet metal is spot welded to one surface of a thin sheet metal structural element such as the inner surface of a door panel of an automobile to provide a composite structure having increased stiffness and higher strength than available from flat sheet metal of equal weight.
U.S. Pat. No. 2,820,228 discloses the use of expanded metal to reinforce and stiffen the bottom of a drawn sheet steel bathtub. The reinforcing is rigidly secured to the outer surface of the bottom panel by welding before the usual enamel coating is applied. Again, the expanded metal reinforcing material is rolled to lie flat against the bottom of the tub, and the two metal components are stated to be preferably rigidly joined throughout substantially their entire contact area, although the patent also states that spot welding can be used if the spot welds are sufficiently close to preclude relative movement upon flexing of the bottom of the tub.
While flat-rolled expanded metal has been used as a reinforcing and stiffening laminate for thin sheet metal as disclosed in the above mentioned patents, substantial bending strength, or stiffening ability, may be lost rolling the expanded metal to the flat state. This may be particularly true for expanded sheets in which the width of the individual strands, i.e., the distance between successive shear lines formed in the material, is substantially greater than the thickness of the original sheet material. When unflattened or unrolled expanded metal is laminated onto a smooth surface, the strands and joints are disposed at a relatively large, acute angle to the cover sheet making the effective thickness of the laminated structure substantially greater than the combined thickness of the cover sheet and the thickness of the sheet material from which the expanded sheet was formed.
Expanded sheet material, as formed on commerical expanding equipment generally has not met widespread use as a stiffening or reinforcing laminate for continuous thin sheets. This is believed to be due, at least in part, to the configuration of the expanded metal which only permits a very small surface area contact between such an expanded sheet and a continuous surface. Such contact is limited to the inclined sheared edges of the joint portion of the expanded metal only, with the edges of the individual strands being spaced from the continuous surface. This limited contact makes effective spot welding or joining by other conventional means very difficult.
U.S. Pat. No. 2,371,754 discloses the concept of stiffening a lightweight, thin sheet material by attaching a uniform pattern of wire to one surface of the sheet of material This patent discloses various forms of welding for attaching the reinforcing wires to the surface of the sheet, and also suggests cementing the wire to the sheet; however, neither the nature of the cement contemplated nor the manner of applying it are disclosed. It is noted, however, that the reinforcing wires are fused together where they are crossed so that, as in the case of the flat-rolled expanded sheet, the wires lay in direct surface-to-surface contact with the sheet metal throughout their full length.